Question

An object 3cm high is placed at a distance of 8cm from a concave mirror which produces a virtual image 4.5cm high. Find the focal length of the mirror


Answer is 24 cm

How

Answer 1

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Explanation: Height of the object (h) = 3 cm

Distance of object from concave mirror (u) = -8 cm

Height of the virtual image formed (h') = 4.5

Let's find 'v' first =

- v/u = h'/h

v = - u × h'/h

v = - ( -8) × 4.5 / 3

v = 12 cm

________

(i) Focal length of mirror = ?

1/f = 1/v + 1/u

1/f = 1/12 + 1/ -8

1/f = -1/24

1 × 24 = -f

24 = -f

f = -24 cm

Answer 2

Explanation:

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